Over the past few days I have encountered a number of users reporting issues with Firefox displaying the below error page:
The proxy server is refusing connections. Firefox is configured to use a proxy server that is refusing connections.
As at the time of this blog entry being written, the issue appears to be specifically related to version 18.0 of Mozilla Firefox. By installing a previous version of Mozilla Firefox (17.0.1), we were able to resolve the problem. Version 17.0.1 can be downloaded from here (Windows version)
In the specific environment that I discovered the issue, the proxy server involved was a Client Side Proxy (CSP) Squid server. The error page above was displayed intermittently on random pages/sites, most of which were using https.
Note: If you install a previous version of Mozilla Firefox, be sure to go into the Options and disable automatic updates for Firefox, otherwise it will simply update itself to 18.0 again automatically.